What Causes Vaginal Bleeding After Using Logynon?

I'm on the contraceptive pill Logynon and I missed the last 4 pills in my previous packet, started the next one a week after and then a few days later started bleeding as if I was having another period but the bleeding is lighter and has gone on now for 8 days instead of 4-5. I know I'm not pregnant and it's not an STD.